1. Field of the Invention
The present invention relates to torque motors having an operating angular range less than 180 degrees (e.g., 90 degrees).
2. Description of the Related Art
Conventionally, for example, a throttle valve may preferably be operated by a torque motor having an operating angular range of less than 180 degrees.
As shown in FIGS. 9 and 10(A), such a known torque motor 101 includes a rotor 110 and a stator 120. The rotor 110 has a center of rotation P110 and comprises a pair of semicircular magnets 112 and 112′. The magnets 112 and 112′ are arranged and constructed so that the outer surfaces thereof respectively have a N pole and a S pole. Thus, the rotor 110 is circumferentially provided with the magnets 112 and 112′ over an angle of 360 degrees. That is, a magnet covering angle of the rotor 110 is 360 degrees, because each magnet may cover the rotor 110 over an angle of 180 degrees. The stator 120 comprises a core 123 and a coil 130. The core 123 has a pair of opposed magnetic pole elements 121 and 122 that respectively have a center P121 and P122. The magnetic pole elements 121 and 122 are arranged and constructed such that a straight line L121 passing through the center P121 and the center of rotation P110 is aligned with a straight line L122 passing through the center P122 and the center of rotation P110 (i.e., such that an angle defined between the straight lines L121 and L122 is 180 degrees).
As shown in FIG. 10(B), the above-described known torque motor 101 thus constructed may have an effective torque generating range of 180 degrees, because the magnets 112 and 112′ are arranged over an angle of 360 degrees. Therefore, the rotor 110 may typically have an effective operational angular range of about 180 degrees. That is, the rotor 110 can rotate clockwise by 90 degrees as well as counterclockwise by 90 degrees from the position shown in FIG. 10(A).
However, as shown in FIG. 9, when the torque motor 101 is used for driving a throttle valve 80, a required or actual operational angular range of the rotor 110 is 90 degrees (i.e., much less than 180 degrees), because the throttle valve 80 may preferably be controlled only through an angular range of 90 degrees. As a result, in the known torque motor 101, as shown in FIG. 10(B), only a portion (i.e., about one-half) of the effective torque generating range is actually utilized in order to operate the rotor 110. In other words, the effective torque generating range of the torque motor 101 may have a “use range” that corresponds to the actual operational angular range of the rotor 110 and a “nonuse range” that does not correspond to the actual operational angular range of the rotor 110.
Thus, the known torque motor has an excessive or unnecessary torque generating range considering that the actual operational angular range of the rotor 110 is only 90 degrees. That is, in the known torque motor 101, the rotor 110 and the stator 120 are not suitably or appropriately designed in compliance with the required or actual operational angular range of the rotor 110. Such a design of the rotor 110 and the stator 120 may interfere with downsizing and weight saving of the torque motor 101.
Another known torque motor is taught, for example, by Japanese Laid-Open Patent Publication No. 1-92541.